In medicine, adhesives are needed for many different purposes, including liquid bandages, wound dressings, skin bonding surgical adhesives, sealants, bioactive release matrixes and implants. Because of the need for sterility in medicine, most medical adhesives are applied from single use adhesive applicators. A popular medical adhesive in a single use applicator is the DERMABOND® medical adhesive developed by Closure Medical Corporation and now sold by Ethicon, a subsidiary of Johnson & Johnson Corporation. As illustrated in FIG. 1 and also described in U.S. Pat. Nos. 5,928,611; 6,099,807 and 6,676,322, an applicator 10 used for the DERMABOND® medical adhesive includes a frangible glass vial 14 held inside a plastic enclosure 16. At the dispensing end of the DERMABOND® plastic enclosure is an applicator tip with a porous plug 18. The porous plug 18 is infused with an accelerator/initiator for accelerating the curing of the DERMABOND® cyanoacrylate adhesive 12. To release the adhesive, one presses on the DERMABOND® plastic enclosure with enough strength to break the frangible glass vial 14. When the frangible glass vial 14 is broken, adhesive slowly flows out of the cracked vial through capillary action and onto the porous plug 18 of the applicator tip. The adhesive can only flow through the porous plug by repetitive squeezing of the plastic enclosure 16. Eventually, the adhesive can be squeezed through the porous plug 18 and applied to the medical use (e.g., sealing a wound). To increase flow rates from squeezing, the DERMABOND® porous tip has been replaced in newer versions with an applicator tip having a porous wafer and a longitudinal hole or lumen. Nonetheless, repetitive squeezing of the plastic enclosure is also required to push adhesive through the porous wafer and longitudinal hole or lumen.
While the DERMABOND® system is in widespread use, it has a number of significant disadvantages. For example, when the DERMABOND® glass vial is crushed, glass shards are created. These glass shards can build up on the porous plug applicator tip. Such a shard build-up can greatly impede the flow of medical adhesive past the build-up. Where the porous plug is replaced by an applicator tip having a longitudinal hole or lumen, the flow of adhesive is increased but so is the possibility of glass shards coming out of the applicator. Obviously, mixing glass shards with medical adhesive is dangerous. Moreover, the flow of adhesive in the DERMABOND® system is difficult to control due to the pressure needed to force the adhesive through the applicator tip. While one can vigorously press on the DERMABOND® plastic enclosure, the DERMABOND® applicator design fails to create a strong, constant force for the adhesive flow. Typically, the adhesive will come out slowly or in spurts—neither of which is desirable in a medical setting where dispensing in a carefully controlled manner is of critical importance. Further, a DERMABOND®-type applicator has a tendency to introduce bubbles into the medical adhesive being dispensed. In adhesives having a water-like viscosity, this is not a big issue because the bubbles tend to break upon emanating from the dispenser tip. However, this is not true for more viscous adhesives, such as the cyanoacrylates used in DERMABOND®, which are activated in the porous plug and, consequently, whose viscosity is already increasing as they are being dispensed.
A form of fluid dispenser is disclosed in May's U.S. Pat. No. 6,641,319 (“May patent”), the disclosure of which is hereby incorporated by reference. Rather than using a glass vial within a plastic enclosure to hold fluid as is done in the DERMABOND® applicator, the May patent creates two chambers in a single plastic enclosure. May's proximal chamber is used to hold unused fluid while May's distal chamber is used to dispense fluid. To separate the two chambers, May places a rupturable membrane between the two chambers in the form of a circular disk with a series of molded radial depressions or weld seams extending from a center point of the disk. When one wants to dispense adhesive from the May applicator, one presses on the outside of May's rupturable membrane until it cracks open and allows fluid to flow from May's proximal chamber to May's distal chamber. With May's membrane ruptured, continued squeezing of May's proximal chamber forces adhesive into May's distal, dispensing chamber and then out of May's applicator altogether.
Even if May's dispenser were used for medical adhesive purposes, May's dispenser would have problems for this application, particularly for cyanoacrylate medical adhesives. Cyanoacrylate monomer compositions, such as those described in Hickey's U.S. Pat. No. 6,743,858, are liquid compositions of monomer that behave like solvents and permeate as well as chemically attack blow molded plastic enclosures made of low-density polyethylene (“LDPE”), mixtures of LDPE and high-density polyethylene (“HDPE”), polypropylene and/or other resins and thus lack the ability to age properly in these containers. The permeation and container wall attack reaction causes the adhesives to polymerize as they age in an applicator made from this group of plastics. By comparison, no permeation occurs in the type of borosilicate glass used in the DERMABOND® frangible glass vials. Due to this permeation and container wall attack in the May dual chamber applicator, cyanoacrylate adhesives typically solidify in several months or earlier in the type of applicator disclosed in May's patent.
Accordingly, there is a need for a medical adhesive applicator where the medical adhesive can be easily dispensed in a controlled manner. There is also a need for a medical adhesive applicator for cyanoacrylate medical adhesives which allows the medical adhesives to not only be easily dispensed but also have a long shelf life.